To recreate: - create a rule on /marc-overlay-rules.pl to protect the 050 tag when staging for MARC import - export a record from your collection and remove the 050 outside of Koha - reimport that record, matching your incoming record to the one already in your collection - confirm the Diff view on manage-marc-import.pl says the 050 will be deleted - complete import, confirm the 050 was retained We should somehow denote when a field will not be impacted due to an overlay rule.